Diagrams are a useful way to efficiently convey abstract information. Layout is an important aspect of diagram creation, impacting heavily on readability. Good diagram layout is difficult because it encompasses both a user's aesthetic preferences as well as drawing conventions for particular styles of diagrams. Existing diagram authoring software provides some layout tools, but these usually perform a once-off change. As such, the author of the diagram handles the majority of diagram layout manually.
We present persistent layout tools for user-specified placement. These tools are implemented with constraint solvers that maintain spatial relationships for the user, throughout further editing. The tools have been designed to be highly usable, with focus on their behaviour, interface and user interaction. We describe the evolution of these tools – which were originally implemented as a plugin for Microsoft Visio – as well as the results of several user studies evaluating their use. We also describe automatic object-avoiding connectors, both poly-line and orthogonal, that allow user specification of style and behaviour via routing penalties.
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